Vehicles provide various conveniences to people but have many factors which threaten a safety of a passenger or a pedestrian. Therefore, vehicles are developing to improve not only the convenience but also the safety, in recent years.
As a representative technology among technologies which improve the safety of the vehicle, a vehicle collision preventing technology using an automotive radar is suggested. A radar is a sensor which transmits an electromagnetic wave and receives a reflected wave to detect and trace a distance from a target, a speed, and an angle and has been mainly used for a military purpose in the related art, but the utilization range of the radar is broadened to be used for a vehicle.
The automotive radar is mounted at a front side or a rear side of the vehicle to detect or trace another vehicle, a pedestrian, a bicycle, or a structure near the vehicle for smart cruise control (SCC) and active safety control. The automotive radar uses a frequency signal of a millimeter wave band having a frequency band of 30 to 300 GHz. The millimeter wave has a very short wavelength of 1 to 10 mm so that when transmission loss in spatial transmission is large and a transmission distance is extremely short (for example, within 10 m). However, when the millimeter wave is used, a size of a circuit or a component may be reduced and a high resolution radar may be configured.
FIG. 1 illustrates a schematic configuration of a general automotive radar.
As illustrated in FIG. 1, the automotive radar mainly includes a transmitting unit 10 and a receiving unit 20 and a number of channels of the receiving unit 20 may be variously set in accordance with a demand of an automotive radar system.
The transmitting unit 10 includes a transmission RF module (TRF) which generates an electromagnetic wave and a transmission antenna (TANT) which radiates the electromagnetic wave which is generated in the transmission RF module (TRF). A plurality of channels of the receiving unit 20 includes a reception antenna (RANT) which receives a reflected wave of the electromagnetic wave radiated from the transmitting unit 10 and a reception RF module (RRF) which receives and analyzes the reflected wave which is incident through the reception antenna (RANT).
That is, the transmitting unit 10 and the plurality of channels of the receiving unit 20 have configurations in which the RF modules TRF and RRF are basically connected to the antennas TANT and RANT, respectively. The RF modules TRF and RRF and the antennas TANT and RANT are connected to transmission lines TL, respectively and the transmission lines are connected by a waveguide, generally, a standard waveguide (SW).
In the recent automotive radar system, the antennas TANT and RANT and the transmission lines TL are embodied using a SIW in many cases.
FIG. 2 illustrates a basic structure of a general SIW.
As illustrated in FIG. 2, a SIW 30 is embodied by disposing a plurality of vias 32 in a dielectric substrate 31, such as Teflon, with a regular pattern and metal grounded surfaces are disposed in an upper portion and a lower portion of the dielectric substrate. As illustrated in FIG. 2, when a plurality of vias is arranged in the dielectric substrate 31 in two lines, a signal may be transmitted between two via lines in the dielectric substrate 31 with a reduced loss. This is because a radiation loss is not caused in the SIW having a structure closed by upper and lower metal grounded surfaces and the via lines, which is different from the transmission line which is partially open, such as a microstrip line of the related art. That is, the dielectric substrate between via lines may function as a transmission line.
Therefore, the SIW 30 may be embodied by disposing the plurality of vias 32 along a path in the dielectric substrate 31 through which a signal is transmitted. The SIW 30 have a simple structure and may be embodied using general printed circuit board (PCB) process, so that mass production may be achieved. The SIW 30 is mainly used as a transmission line for a high frequency band signal such as a millimeter wave.
In the meantime, the waveguide SW is used as a millimeter wave transit device for connecting the transmission lines with a reduced loss, as described above. However, in order for the waveguide SW to connect the transmission lines TL embodied by the SIW with a reduced loss, it is necessary to embody a transit structure which easily transits the millimeter wave from the SIW to the waveguide SW. In order to save cost for the radar system and reduce a size of the radar system, the transit structure needs to have a simple structure and be embodied using a general PCB process without having an additional structure other than a substrate which embodies the SIW. Further, a signal transition characteristic in accordance with the transit structure needs to have a frequency band which is sufficiently broader than a frequency which is operated by the radar system and uniformly transit signals in the frequency band as much as possible.
Korean Registered Patent No. 10-0714451 (titled “Transition structure of SIW and standard waveguide”) discloses a transition structure in which a cavity is formed between a waveguide and a SIW to easily establish matching therebetween, but a separate substrate needs to be added to form the cavity and a process of bonding the dielectric substrates is added, which increases cost.
Further, “Broadband Ka-band rectangular waveguide to substrate integrated waveguide transition” (Electronics Letters, Apr. 24 2013)” suggests a transition structure which includes two resonating slots (dual resonating slot) to directly connect the waveguide and the SIW to each other. Such a transit structure has advantageously a broad band width (6.6% with respect to a relative band width) as compared with a transit structure including one resonating slot but does not have a uniform signal transit characteristic for a frequency due to an influence of a transmission characteristic of the dual resonating slot.